The invention relates to spade assemblies suitable for use on artillery such as vehicle-mounted mortars and howitzers.
In artillery vehicles such as mortars and howitzers, considerable recoil forces are generated as a fired projectile leaves the weapon mounted on the vehicle. The common approach in dealing with recoil forces is to fit so-called spade assemblies to the vehicle so that it is braced during firing.
The spade assemblies are typically arranged as two arms pivotally mounted to one side of the vehicle and positioned so that they penetrate the soil. This arrangement transfers recoil forces from the weapon to the ground, and discourages the vehicle from moving under the influence of recoil forces.
Many artillery vehicle are often relatively light in weight in relation to the significant recoil forces that can be generated during firing. In many cases, a weapon is mounted on a vehicle chassis or other wheeled structure which is easily displaced by recoil forces. Accordingly, spade assemblies are typically an important component of such vehicles or other wheeled structures.
The use of spade assemblies is associated with various shortcomings. During recoil, the spade assemblies tend to compress the soil on which they act, and the vehicle tends to return to its former position after firing. Accordingly, a gap is formed between the spade assembly and the soil.
Subsequent refiring causes the spade assembly to come into contact with the soil again, after the gap between the spade assemblies and the soil is closed. This can cause considerable stresses in the spade assemblies and in the structure of the vehicle mounting. These stresses can cause significant damage and possible failure if appropriate structural reinforcements are not provided.
Further, free-play between the spades and the soil can reduce the accuracy of firing. When low-fire rate accuracy is required, one approach has been to ure-layn the weapon to compensate for angular shifts of the vehicle after each firing.
It is an object of the invention to address these and other deficiencies associated with existing spade assembly arrangements.
The invention provides a self-compensating spade assembly suitable for use on a vehicle having a mounted weapon generating a recurring recoil force, the spade assembly including:
an elongate spade arm;
a spade mounting at one end of the spade arm for mounting the spade to the vehicle; and
a ground contacting portion at the other end of the spade arm, the ground contacting portion including a support plate and a spade portion which are mutually positioned so that when the spade assembly is in use, the spade portion penetrates the earth on which the weapon is standing, and the support plate rests against the earth to at least partly transfer recoil forces from the weapon to the earth;
characterised in that the spade arm has a compensating means able to regulate the length of the spade arm to ensure that the ground contacting portion is generally maintained in firm contact with the earth on which the weapon is standing.
Preferably, the compensating means includes a telescopic engagement of two relatively slidable members defining a sealed chamber containing a source of hydraulic or pneumatic pressure which acts to bias the spade assembly in an extended position.
Preferably, the spade assembly can be maintained generally rigid in compression when the weapon is being repeatedly fired. Preferably, this is achieved by the use of an automatic locking arrangement which ensures that, during use, the length of the spade assembly can be increased but not decreased. Preferably, this is achieved by providing a hydraulically actuated system in which the volumes of distinct chambers are adjusted by regulating the flow from one chamber to the other, thus adjusting the relative position of the slidable members.
The invention further includes a vehicle having mounted thereon one or more spades according to the first aspect of the invention.
Preferably, two spade assemblies are used in combination to assist in stabilising a vehicle during recurrent firing. Preferably, the spade assemblies are in use angularly orientated at 40xc2x0 below horizontal, and mutually positioned so that they define an included angle of 90xc2x0. This outwardly defined assists in stabilising the vehicle against recoil forces acting laterally as well as transversely of the weapon.